| Arcovenator | |
|---|---|
 | |
| Braincase (MHNAix-PV 2011-12) in dorsal view | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Abelisauridae |
| Subfamily: | †Majungasaurinae |
| Genus: | †Arcovenator Tortosaet al., 2014 |
| Species: | †A. escotae |
| Binomial name | |
| †Arcovenator escotae Tortosaet al., 2014 | |
Arcovenator ("Arc hunter") is anextinctgenus ofabelisauridtheropoddinosaurs hailing from theLate Cretaceous ofFrance and possiblySpain.[1][2] Thetype and only describedspecies isArcovenator escotae.[1] Its name derives from theriver Arc flowing near the site of its first discovery.
Though shallower, the nearly completebraincase ofArcovenator is otherwise similar in size to those ofMajungasaurus andCarnotaurus; it was thus initially estimated as being about 5–6 m (16–20 ft) long,[1] but it was estimated in 2016 as being 4.8 m (16 ft) in length.[3] Theskull roof exhibits as aunique diagnostic character a midlineforamen, possibly housing thepineal gland, situated on the posterior surface of a slight dome formed byfrontal bones as moderately thick as inAucasaurus, thus less so than forRajasaurus, though more than those ofRugops.[1] Less characteristically, above theorbit is a lowfossa with a smallfenestra bordered by thelacrimal, frontal, and postorbital.[1] Theparietal bordering the supratemporal fenestrae forms ridges medially on the latter's respective anteromedial margins which, as they approach theparietal eminence, fuse into asagittal crest.[1] Thepostorbital is intermediate between theplesiomorphicT-shaped condition ofEoabelisaurus and the derived invertedL-shaped one ofCarnotaurus due to the unique feature of having a sheet of bone linking its ventral and posterior processes.[1] It has, in a similar autapomorphic fashion, a thick, rough-surfaced process dorsal to the eye socket that extends to the lacrimal, forming a bonybrow ridge, and in a less notable way, a lateral rugose tuberosity on the extremity of its ventral process.[1] The paroccipital processes have remarkable accessory dorsal and ventral bony bars, that thus bound depressions lateral to theforamen magnum.[1] Theear region closely resembles that ofMajungasaurus, though differing most substantially on a laterally directed basipterygoid process, with the shorter crista prootica and the smaller extent of a groove anterior to the2nd and3rd cranial nerve foramina being minor deviances from Majungasaurinae's type.[1] Thesquamosal is similar to that of the latter except for a less prominent parietal process.[1] Generally, the external bone ornamentation is more subdued than that ofMajungasaurus.[1] The tall teeth (3-5.5 cm) have denticles on the apical portion of themesial carina and along the length of the distal one, with varying density.[1]
Thecaudalvertebrae ofA. escotae are remarkably similar to those ofMajungasaurus, though more dorsoventrally compressed.[1] The centra possess amphicoelous articulations with the pertinent facets of an intermediate nature between the circular ones ofIlokelesia and those of the elliptical shape inRajasaurus and have neither pneumatic recesses nor accessoryhyposphene-hypantrum articulations.[1] Thetransverse processes of theneural arches are not as inclined as in theBrachyrostra.[1]
Thecnemial crest ofArcovenator's theslender 51-cmtibia is well developed as is characteristic ofabelisauroids.[1] It has a proximallateral condyle more prominent than themedial one, a slight anterodorsal curve on the proximal aspect of the fibular crest, a noticeable distal longitudinal ridge, and taperedmalleoli.[1] The nearly half-meter-longfibula possesses the typical anatomical characters ofceratosaurs.[1]
Arcovenator is a theropod genus nested within the cladeAbelisauridae,[1] which inLinnaean taxonomy has the rank offamily.[4] This taxonomical group has as close relativesnoasaurids within theAbelisauroidea.[1][5] The latter in turn along withLimusaurus andCeratosaurus nests withinCeratosauria.[1][6]
Distinguishing characters of abelisaurids are their short, tall skulls with extensively sculptured external surfaces, the drastically reduced fore limbs, and the stout hind limbs.[7]
Thierry Tortosa and colleagues conducted aphylogenetic analysis, which is summarized in thecladogram below and is based, in part, on previously published works including both the newly discovered fossil remains and other described but unnamed French abelisaurs.[1]
| Majungasaurinae |
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The study generally agrees with previous results, namely a relatively recent one obtained both by Matthew Carrano and Scott Sampson (2008)[8] and Diego Pol and Oliver W. M. Rauhut (2012)[6] of a clade that includes at leastMajungasaurus,Indosaurus andRajasaurus, which in the more recent analysis includesArcovenator.[1] Tortosaet al.. name this well-supported clade theMajungasaurinae, ranking it assubfamily and defining it to contain all abelisaurids more closely related toMajungasaurus than toCarnotaurus.[1] The members of this taxonomical group have various cranial characters in common including an elongated antorbital fenestra, and a parietal with a sagittal crest that widens anteriorly into a triangular surface.[1] Also of note is that, in partial agreement with some analyses, the more fragmentary French ceratosaur remains are placed within Abelisauridae, and contrary to others,Abelisaurus is recovered as acarnotaurin.[1]
Also, insights into thepaleobiogeography of abelisauroids exist; just presence of them in the so-called European Archipelago[9] confounds hypotheses that only consider the continents derived from thebreakup ofMesozoicGondwana.[1] Two lineages of European abelisaurs are discerned: a basal one, including the smallAlbianGenusaurus and LowerCampanianTarascosaurus, and a derived one, the larger CampanianArcovenator allied with theMadagascanMajungasaurus and theIndianRajasaurus in Majungasaurinae.[1] As the inferred character distributions obtained through the phylogenetic analysis make it unlikely that these lineages are more closely related to each other than to other abelisaurids, this suggests a more complicated series of events regarding their biogeography withvicariance applicable to the older one and oceanicdispersal being likelier for the more recent one.[1] These results lend support to the proposed role of Africa as a hub for faunal movements betweenEurope and India or Madagascar[10] and the isolation of South American abelisaurids.[1][8]
The fossil remains ofA. escotae were found nearPourrières,Vardepartment,Provence-Alpes-Côte d'Azurregion, during preventive paleontological and archaeological prospection activities before construction took place on the stretch of theA8 motorway betweenChâteauneuf-le-Rouge andSaint Maximin.[1][11][12] The pertinent lateCampanian strata (between 72 and 76million years ago)[13][14][15] of the LowerArgiles Rutilantes Formation are located in theAix-en-ProvenceBasin of southeasternFrance.[1] Theholotype ofArcovenator escotae, housed at theMuséum d’Histoire Naturelle d’Aix-en-Provence, was found closely associated in a single stratum of fluvial sandstone and is made up of specimens MHNA-PV-2011.12.1, a braincase in articulation with a right postorbital, MHNA-PV-2011.12.2, a left squamosal, MHNA.PV.2011.12.15, a tooth, MHNA.PV.2011.12.5, MHNA.PV.2011.12.5, an anterior caudal vertebra, MHNA.PV.2011.12.3, a right tibia, and MHNA.PV.2011.12.4, a right fibula.[1] Two anterior caudal vertebrae (MHNA.PV.2011.12.198 and MHNA.PV.2011.12.213) and three teeth (MHNA.PV.2011.12.20, MHNA.PV.2011.12.187 and MHNA.PV.2011.12.297) found close both in distance and depth were also referred to the species, but belonging to different individuals.[1] It is likely that a maxilla, the sole fossil found of the so-calledPourcieux abelisaurid, is referable to at least this genus on account of both its close proximity in time and space and the results of the phylogenetic analysis.[1][8] Numerous abelisaurid teeth from the earlyMaastrichtian strata fromLaño are referred to asArcovenator sp.[2]
The genus nameArcovenator derives from the riverArc as the locality is set within itsbasin and theLatin word for hunter,venator.[1] Thespecific epithet 'escotae' honorsEscota, amotorwayconcession company,[16] which since 2006 has provided the necessary funds to excavate the locality.[1]
A. escotae lived on the Ibero-Armorican island,[1] a relatively large landmass formed by what are now parts of France,Spain, andPortugal.[9] Thecompressionalsubsidence basin of Aix-en-Provence was a low-reliefendorheic affair located at apaleolatitude of 35°N, and had its borders to north and south in the form oflimestonehighlands, respectively theSainte Victoire andEtoile massifs, and to the east as the Maure Mountains.[13] The sediment from these sources flowed along rivers into a perenniallake originating interbedded lacustrine, alluvial and fluvial sediments at the time ofArcovenator, when the climate was warm, subhumid with marked seasons.[13] The fossil remains were found in one of theformation's various levels of fluvialsandstone,[1] characteristic of ariver's mouth or when itoverflows its banks,[13] along withhybodonts, theturtlesFoxemys andSolemys, thecrocodylomorphsMusturzabalsuchus andIschyrochampsa,azhdarchidpterosaurs,titanosauriansauropods, theornithopodRhabdodon andnodosaurids.[1] The abundance of fragmentary remains of medium-sized abelisaurs, especially teeth in this and other localities of the region show that these animals would have been relatively common in the landscape.[1]
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